Elongated cylindrical tensile articles of the type useful as flylines, are usually manufactured from a polymeric monofilament, a single or multistrand polymer filament core surrounded by a usually extruded polymer covering such as polyvinyl chloride, or a braided polymer or glass filament. The overall density of the line determines whether or not the line floats on the surface of water or sinks in water.
The flyline itself may be of a sinking or floating type or may be a generally floating line with a sinking tip or may be level (having no taper) or tapered in various segments of its length to achieve weight distributions deemed favorable for more accurate placement of a fly or for easier placement of the fly at a longer distance from the angler. Fly fishing lines are usually up to about 105 feet in length. This length is typically secured to a length of small diameter backing line which is first wound onto the reel ahead of the flyline to give extra length as necessary for casting the flyline or playing a hooked fish.
To provide a floating line, one method used at the present time is to surround a core by a polymer layer containing as filler a quantity of hollow light-weight microspheres or microballoons of about 50 to 250 micron diameter. These microballons are available in various diameters, compositions, and densities and are typically of plastic or glass composition. Such microballoons may be prepared by methods disclosed in U.S. Pat. No. 2,797,201, for instance. An additional layer of polymer containing no filler, or a lesser quantity of microballoon filler, may surround the inner or first layer to provide a smoother more durable skin on the line and to give a less stiff or more flexible line.
In contrast, a sinking line may contain components of density greater than one or contain a heavy filler to achieve that higher density.
Other descriptions of presently available fly-casting lines and their methods of manufacture may be found described in U.S. Pat. Nos. 3,841,015; 3,868,785 and 4,524,540, an article by Mosser in "Fly Fishing," June 1989, pages 85-87, and an additional article in "Fly Fisherman," Dec 1989, pages 38-43, 60-61.